Undercoordinated indium as an intrinsic electron-trap center in amorphous InGaZnO4

Undercoordinated indium (In*) is found to be an intrinsic defect that acts as a strong electron trap in amorphous InGaZnO4. Conduction electrons couple with the under-coordinated In* via Coulomb attraction, which is the driving force for the formation of an In*–M (M=In, Ga, or Zn) bond. The new structure is stable in the electron-trapped (2–) charge state, and we designate it as an intrinsic (In*–M)2− center in amorphous InGaZnO4. The (In*–M)2− centers are preferentially formed in heavily n-doped samples, resulting in a doping limit. They are also formed by electrical/optical stresses, which generate excited electrons, resulting in a metastable change in their electrical properties. Korean scientists have identified a key clue that can enhance the long-term stability of transparent semiconductors in ‘wearable’ computers. Recently, a glass-like oxide containing the metals indium, gallium and zinc (InGaZnO4) has found wide use in flexible electronic devices because its speedy transistor characteristics can drive high-resolution optical displays. However, the capabilities of this see-through semiconductor often degrade over time due to a phenomenon called charge trapping. Yong-Sung Kim from the Korea Research Institute of Standards and Science and co-workers simulated the amorphous structure of InGaZnO4 by performing first-principles quantum computations and discovered a previously unnoticed trapping site — ‘under-coordinated’ indium atoms that snare extra electrons through strong electron–ion interactions. Processing conditions that specifically supress populations of under-coordinated indium should be an essential part of future manufacturing efforts, suggest the authors. Undercoordinated indium (In*) is found to be an intrinsic defect that acts as a strong electron trap in amorphous InGaZnO4. Conduction electrons couple with the under-coordinated In* via Coulomb attraction, which is the driving force for the formation of an In*–M (M=In, Ga, or Zn) bond. The new structure is stable in the electron-trapped (2–) charge state, and we designate it as an intrinsic (In*–M)2− center in amorphous InGaZnO4. The (In*–M)2− centers are preferentially formed in heavily n-doped samples, resulting in a doping limit. They are also formed by electrical/optical stresses, which generate excited electrons, resulting in a metastable change in their electrical properties.